Revert "Enable code-owners for All-Projects"

This reverts commit 83468030cb862f365bd04e3d4814aa710ffc6404.

Reason for revert: Broken OWNERS files.

Original change's description:
> Enable code-owners for All-Projects
>
> Fixes: b/216440912
> Change-Id: If6618cdaa2a01a9dfe4f1e503c0fa3d7a57e261d
> Reviewed-on: https://dart-review.googlesource.com/c/All-Projects/+/235022
> Reviewed-by: William Hesse <whesse@google.com>

TBR=whesse@google.com,athom@google.com

Change-Id: I3505f7e3f3a27f30ad0fb89000c2074d68f4d2ac
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/All-Projects/+/235120
Reviewed-by: Alexander Thomas <athom@google.com>
Reviewed-by: William Hesse <whesse@google.com>